Moveable or roaming objects, including persons and animals, may be required, for various reasons, to be located by a third party or system, from a remote location. Examples for such needs may include persons in distress, particularly children, adults or handicapped people that require assistance, lost pets, stolen vehicles to be restored and transported assets to be tracked on their way.
A conventional technique for locating roaming objects from remote location(s), involves utilizing wireless devices that are attached to these objects, in advance, and a radio network capable of communicating with these wireless devices and transmitting signals from which their location may be interpreted by a remote receiver. The communication channels in such network may comprise wireless and wireline elements, and the components of the network/system may be terrestrial, extraterrestrial airborne and space-borne. In some cases, this wireless location network serves also for telecommunications (“telecom”) of generic information, such as voice, data or video signals.
One particular framework for wireless location is promoted by the U.S. Federal Communications Commission (FCC), in order to locate cellular handsets operated by people in emergency situations. This plan is known as the “E911” act, an augmentation to the “911” service (a service that is provided in the U.S.A.), designed to handle distress calls, either from fixed or from mobile phones. Currently, the 911 service is capable of locating fixed phones, while in the future it is planed to be capable of locating mobile phones as well, for the same purpose of emergency assistance. For further information, see: http://www.fcc.gov/e911/ and also CFR (Code of Federal Regulations) Title 47, Volume 2, Parts 20 to 39, [Revised as of Oct. 1, 1999] PART 20-COMMERCIAL MOBILE RADIO SERVICES—Sec. 20.18-911 Service.
Several methods are known in the art for wirelessly determining the location of roaming devices. One known group of methods is based on dedicated Telecom networks or dedicated segments of a Telecom network. These methods are usually referred to as “network based”, i.e., they employ a wide area array of antennas and transceivers coupled together, such that a roaming wireless device can be located whenever being contained within the area that is covered by said antennas. Such methods usually require minimal modifications in the communication devices the location of which is to be determined by this network.
The latter methods are further subdivided into “sub-methods”. One such sub-method measures the Angle of Arrival (AOA) of a signal emitted by a roaming wireless device, received at least at two of the network's antennas. Knowing the location of these antennas and the AOA of the received signal, the location of the roaming wireless device can be derived by trigonometric calculations.
Another sub-method measures the Time of Arrival (TOA) of a signal emitted by the roaming wireless device, received at least at three of the network's antennas. Knowing the location of these antennas and the TOA of the received signal, the location of the roaming wireless device can be derived. The TOA method is based on spherical radio navigation, i.e., the geometric locus of points having a same range from a fixed point is a sphere surface, the fixed point of which is its center. In case of TOA, the fixed points are the receiving network's antennas and the range is [TOA×C] for each receiving antenna, wherein “C” is the velocity of light or electromagnetic waves. The location of the roaming device is calculated as one of the two points, defined by the crossing sector of all three sphere surfaces (the crossing sector of two spherical surfaces is a circle, and this circle crosses a third sphere surface at two points). Sometimes, a fourth antenna is used to remove this ambiguity or to compensate for clock discrepancies.
The Global Positioning System (GPS), as described hereinafter, is based on a TOA method as well. In addition, if the roaming device is known to be essentially on the ground (e.g., mounted in a car), the earth globe, with proper topography, can be used as an additional reference “sphere” to refine the TOA calculations. This approach is especially useful for GPS navigating vessels, particularly in oceans, where the altitude is constant (i.e., is the sea level).
One useful variation of TOA is TDOA (Time Difference Of Arrival), where a difference in time of arrival of one transmitted signal is measured at two different receivers. This method was originally developed for radio navigation systems as LORAN-C and OMEGA, however slightly different—the time difference between two signals, transmitted synchronously from two remote sites, is measured at the LORAN-C or OMEGA receiver. Both variations of TDOA are based on hyperbolic radio navigation, i.e., the geometric locus of points that have a common difference in range from two fixed points is a hyperbola. In TDOA, as in TOA and GPS, time measurements provide range estimation (“pseudorange”), since [time×C=range]. In order to determine the actual location of a moveable device by TDOA, at least three reference antennas are required, to provide two hyperbolas that cross each other at one point, being the required actual location. For further information, see the book “AMERICAN PRACTICAL NAVIGATOR” by N. Bowditch, Pub. No. 9, volume 1, part eight (ELECTRONICS AND NAVIGATION), published by the DEFENSE MAPPING AGENCY HYDROGRAPHIC CENTER, USA DoD.
An exemplary system that utilizes TDOA and AOA methods for location determination is Sigma-5000 TDOA-AOA, which has been developed by “SigmaOne” (Rehovot science park, Israel). See also www.sigma-1.com/index_flash.htm. However, network-based methods for wireless location determination, require a dedicated infrastructure of antennas and transceivers, which is costly and takes substantial time to deploy.
Another known group of methods for wirelessly determining the location of roaming devices is based on self-location capabilities incorporated in the Telecom end unit (e.g., a wireless “handset” device). The unit location can be measured at the unit itself by utilizing corresponding sensors, embedded in the unit. Then, a signal representing this location is transmitted wirelessly over the network to a place where it is required. These methods are usually referred to as “handset based”.
One handset based sub-method uses a GPS receiver embedded in a mobile Telecom unit. A GPS receiver measures its position by processing signals received from navigation satellites, launched by the U.S. Department Of Defense (DOD). Signals from at least 4 satellites are required to reach the antenna of the GPS receiver, in order to allow calculating its location. GPS technology is based on a TOA method, however slightly different—multiple transmissions are received at a single receiver. Due to clock discrepancies between satellites and GPS receivers, at least four in-view satellites are required in order to determine a GPS position (only three are required if the altitude is known, as in case of ocean navigation).
The GPS geographic position is expressed in latitude and longitude coordinates, in addition to altitude above sea level. GPS uses the World Geodetic System defined in 1984 (“WGS-84”). Though there are about 100 different local grids in use by cartographers in different parts of the world, in addition to different map projections, WGS-84 coordinates can be converted to any other reference grid.
GPS receivers have two different versions, military (P code) and civilian (C/A code). After the removal of the intentional degradation—“Selective Availability” (S/A) from the GPS signals, a C/A code GPS receiver can typically achieve an accuracy of better than 50 meters (rms). This position, practically expressed in about 10 bytes, can easily be transmitted over the network, by the same Telecom unit that contains the GPS receiver, to a place where it is required. For further information one might reference the web site www.trimble.com/gps/.
Examples for such prior art technologies are products of “SiRF” (California, U.S.A.) Particularly, those following SiRF's handset-based SiRFstar TM architectures SiRFstarI and SiRFstarII. For further information one might reference the web site www.sirf.com/.
Other prior art systems introduce capabilities for short-range wireless connectivity in cellular handsets and mobile computers. This type of connectivity is normally required for forming wLANs (wireless Local Area Networks) or wPANs (wireless Personal Area Networks), while the primary cellular network is usually referred as wWAN (wireless Wide Area Network). Usually, wLANs support faster data rates and larger transmission distances than wPANs. The typical state of the art of a wLAN transmitter range is about 500 meters, while a wPAN transmitter range is typically 10–100 meters. One specific standard for wLANs is IEEE 802. 11. WPANs typically replace short communication cables, supporting wireless handset peripherals, such as a keyboard, screen/display, headset, speaker and microphone, or data communications between a cellular handset and a Personal Digital Assistance (PDA), e.g., for updating a telephone list. One of the standards for short-range wireless connectivity (wPAN) is “Bluetooth” (“BT”), originally defined by Ericsson, Sweden, which utilizes wireless digital connectivity over the 2.4 GHz unlicensed band, using frequency hopping spread spectrum modulation, at 721 Kbps (revision 1.1). No line of sight is required between a transmitter and a receiver and the typical communication range is 10–100 meters, depending on which transmission class, chosen from one of the three available classes of maximum RF power, is in use: 1 mw (class 3), 10 mw (class 2) or 100 mw (class 1). Several schemes of power saving, error correction, authentication and encryption are included in the BT standard. Each BT device is assigned a unique 48 bits ID. BT devices form ad hoc “piconets”, even among devices that have no previous coordination, with up to 8 peer devices, one of which is considered a master device. Basically, the unit that initiates the connection is defined as master of the piconet. However, these roles can be switched over. For further details, one might reference the web site www.Bluetooth.com.
Currently, state of the art of BT technology allows the implementation of almost a full BT digital radio, including RF and baseband circuitry, in a smaller than 10×10 mm chip size. For example, see Cambridge Silicon Radio (CSR) “bcO1” chip, Philips “PCD 87750” or Ericsson's “PBA 3131” radio chip.
Since BT chips are also low power consumers, typically 100 mw in active mode (receive or transmit—class 3) and about 1 mw in standby mode (“page scan” or “inquiry scan” or “park”), they fit battery operation, and particularly designed to be embedded in cellular handsets and portable computers.
Several models of BT-enabled cellular handsets have already been introduced to the market, as “Ericsson R520”, “Nokia 6310” and “Motorola Timeport 270c”.
U.S. Pat. No. 6,246,376 discloses a method for refining GPS positioning by data provided over a Bluetooth (BT) connection, or by the BT received signal. This method might be utilized, for example, for measuring azimuth. A cellular handset is utilized, which includes a GPS receiver, a BT radio and additional navigation circuitry, for example a “north-finder”/compass. Such handset calculates its position by GPS, while utilizing also the received BT data signal. However, handset-based wireless location devices are expensive, consume a considerable amount of power, are relatively big in size and radiate substantial RF power.
There is another group of known methods for wireless location, which is based on a combination of network and handset based capabilities. Such methods are usually referred to as “hybrid solutions”. For example, WO/0150151 discloses a way for locating cellular handsets that include a GPS receiver. The data received by the GPS receiver is enhanced, particularly when satellites are blocked, by providing positioning data by nearby Bluetooth base stations.
Many wireless location systems are deployed and expected to be further deployed in the future, particularly systems to locate cellular handsets over cellular networks. The urge for the deployment is driven by Federal and state regulations, as well as by the need for location based commercial services.
All the methods described above have not yet provided satisfactory solutions to the problem of wirelessly determining the location of small, inexpensive and low power roaming devices, over a wide area, without requiring a dedicated infrastructure.
It is an object of the present invention to provide a system and method for wirelessly determining the location of devices, by leveraging the location determining capability of conventional positioning systems, such as those used to locate cellular handsets, to determine the location of a different type of wireless devices, smaller and cheaper, by wirelessly linking between both types of devices.
It is another object of the present invention to provide a system and a method for wirelessly determining the location of devices, by utilizing existing and widespread active Telecom units (“communication devices”), such as mobile telephones, to be used as gateways or access points for a second tier of wireless devices, forming a large and dense mobile communication infrastructure for said wireless devices, over a wide area.
It is still another object of the present invention to provide a system and a method for wirelessly determining the location of devices, by utilizing the existing infrastructure of a communication network having positioning capabilities.
It is yet another object of the present invention to provide a system and method for wirelessly determining the location of roaming objects in an area covered by a Telecom network, by using location determining devices which are small, inexpensive and having low power consumption.
It is yet another object of the present invention to provide a system and method for wirelessly determining the location of roaming objects in an area covered by a Telecom network, by using location determining devices, which emit low RF radiation and reduce potential risk to their carriers.
It is yet another object of the present invention to provide a system and method for wirelessly determining the location of roaming objects in an area covered by a Telecom network, by using location determining devices which do not require human interface/intervention.
It is yet another object of the present invention to provide a system and method for wirelessly determining the location of roaming devices, in an area covered by a Telecom network, that minimizes the amount of data that should be transmitted over the Telecom network.
Other objects and advantages of the invention will become apparent as the description proceeds.